Tungsten ring composition

ABSTRACT

A method of forming a jewelry article comprises the steps of (a) providing a powder mixture comprising tungsten and one or more of: titanium carbide, chromium carbide, nickel, molybdenum, vanadium carbide and iron, (b) placing the powder mixture in a mold and (c) applying sufficient pressure and temperature to the powder mixture to form a solid jewelry article.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of ______ filed on 14 Jun. 2008 in China, entitled “TUNGSTEN RING COMPOSITION”, the contents of which are incorporated by reference herein.

BACKGROUND

The present invention generally relates to the field of jewelry articles and specifically jewelry articles comprising tungsten.

There is a need in the jewelry industry for a durable jewelry article that comprises mainly of tungsten but is free of tungsten carbide. Furthermore, the currently available tungsten carbide articles, such as jewelry rings, typically exhibit a dark gray luster. For aesthetic purposes, it is advantageous to be able to offer jewelry articles based on tungsten with different color tints.

SUMMARY

In one embodiment, a method of forming a jewelry article comprises (a) providing a powder mixture comprising tungsten and one or more of: titanium carbide, chromium carbide, nickel, molybdenum, vanadium carbide and iron, (b) placing the powder mixture in a mold and (c) applying sufficient pressure and temperature to the powder mixture to form a solid jewelry article.

In another embodiment, a jewelry article comprises less than 50% by weight tungsten and balance titanium carbide, chromium carbide, nickel, molybdenum, vanadium carbide and iron.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flow diagram illustrating the steps in the manufacture of a jewelry article, in accordance with one embodiment.

FIG. 2-3 are images of jewelry article manufacture equipments, a powder mixture and raw jewelry articles.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the present embodiments, a method of forming a jewelry article comprises (a) providing a powder mixture comprising tungsten and one or more metallic and/or ceramic component(s), (b) placing the powder mixture in a mold and (c) applying sufficient pressure and temperature to the powder mixture to form a solid jewelry article. Thus, the jewelry article formed according to the present embodiments comprises tungsten and one or more metallic and/or ceramic components.

Powder Mixture

In one embodiment, the powder mixture comprises tungsten and one or more of: titanium carbide (TiC), chromium carbide (Cr₃C₂), nickel, molybdenum, vanadium carbide (VC) and iron. In the preferred embodiments, the powder mixture comprises tungsten, titanium carbide, chromium carbide, nickel, molybdenum, vanadium carbide and iron.

The weight percentage range of each component in the mixture may vary depending on the desired physical properties and/or aesthetic appearance of the jewelry article. In general, the weight percent of tungsten in the mixture is less than about 50%. Preferably, the tungsten weight percent is about 20-50%, and most preferably about 40-50%. The powder mixture may comprise about 15-25%, preferably about 21-22% titanium carbide. The chromium carbide content may be about 15-25%, preferably about 19-21%. Additionally, the nickel content may be about 15-25%, preferably about 22-23%. Further, molybdenum and vanadium carbide combined amount may be about 5-10%, preferably between 7-8%. Finally, the iron content may be about 1-5%, preferably about 2-3%. All percent ranges described herein are by weight and include every individual value within each range.

In a non-limiting example, the mixture comprises about 21-22% titanium carbide, about 20% chromium carbide, about 45% tungsten, about 22-23% nickel, about 7-8% molybdenum and vanadium carbide combined, and about 2-3% iron.

In one embodiment, the powder mixture is prepared by milling a particle mixture of the components for a sufficient period of time to reduce the size of the mixture particles. In another embodiment, the powder mixture is prepared by combining components that are already in powder form (fine particles). In a further embodiment, in addition to milling, the mixture is also subject to one or more steps of sedimentation/separation, drying and sifting.

In a non-limiting example, a mixture comprising tungsten and one or more of titanium carbide, chromium carbide, nickel, molybdenum, vanadium carbide and iron is milled, followed by sedimentation/separation, drying and sifting steps to form a powder mixture.

In another non-limiting example, a mixture of tungsten and one or more of titanium carbide, chromium carbide, nickel, molybdenum, vanadium carbide and iron, is subjected to (a) milling (b) sedimentation/separation, (c) drying, (d) sifting and again (e) drying to form a powder mixture.

In one embodiment, the powder mixture also comprises at least one rubber material. In one aspect, the rubber assists in binding the powder particles together. In a further aspect, the rubber assist in processing and shaping the powder mixture. Thus, the amount of rubber added may vary depending on the processing and shaping requirements. Examples of suitable rubbers include, but are not limited to, latex rubbers, butadiene rubbers, styrene butadiene rubbers, thermoplastic elastomers and melt processible rubbers. Of course, a combination of different types of rubbers may also be used. Preferably, the rubber material comprises styrene-butadiene-styrne (SBS). However, other similar polymeric materials such as styrene-isoprene-styrene may be equally useful. Where the mixture processing step includes milling, the rubber material is preferably added after the milling step.

In certain cases, the weight percent of tungsten and other components in the powder mixture may differ from that in the raw jewelry article. For instance, addition of other components, such as SBS rubber, may lower the weight percent of the powder mixture components. Still, in some embodiments, the weight percent of the components in the powder mixture and jewelry article maybe about the same.

In the powder mixture, the particle size range is preferably small enough to allow effective sintering of said powder mixture. If needed, particle size may be reduced by running a particle mixture through a sieve, to obtain smaller particle sizes. For instance in a non-limiting example, a mixture is run through one or more sieves with mish hole diameter(s) less than 0.40 mm to obtain a powder mixture with an average particle size of about 1-2 μm.

The density and hardness of the formed article may vary depending on the type and amount of the components. In some embodiments, the formed jewelry article has a density between about 8-9 g/cm³ and a HRC hardness of about 74.0 or higher.

In one embodiment, the powder mixture also comprises components which impart color to the jewelry article. For instance an amount of a nitride may be added to change the color of the article.

Molding/Melting (Sintering)

Once formed, the powder mixture is placed in the cavity of a mold and subjected to elevated pressures to form the raw jewelry article. The mold cavity may be shaped according to any basic jewelry article design. In the preferred embodiments, the mold cavity produces an annular shaped jewelry article. The formed raw jewelry article may comprise one or more facets, grooves, or notches.

In a non-limiting example, the powder mixture is sintered (or melted) in the mold at a temperature of about 1440-1450° C. In yet another non-limiting example, the powder mixture is first heated to about 550° C. before sintering to remove the rubber contents (wax).

After molding, the raw jewelry article may be then subject to further processing steps, such as attaching precious metals pieces or gems to the article.

The flow diagram of FIG. 1 provides a non-limiting example of manufacturing steps 100-118, for forming a jewelry article in accordance with one embodiment. Accordingly, in step 100, a mixture comprising 21.35% TiC, 20% chromium carbide, 45.87% W, 22.68% Ni, 7.54% Mo+VC and 2.18% Fe, is milled in ethanol for 72 hours. In step 102, the milled mixture undergoes sedimentation/separation followed by a drying step 104 at 90-100° C., 1 atm for 2.5 hours. Following a sifting step 106, an amount of SBS rubber is then added to the powder mixture in step 108. This mixture is again sifted resulting in a powder mixture having particles sizes in the range of about 1-2 μm. The first and second sifting steps are carried out using a mesh with 0.19 mm and 0.38 mm diameter holes, respectively. The powder mixture is then dried in step 112 for about 1-1.5 hours and shaped in consecutive molding 114 and melting (sintering) 116 steps. The melting step is carried out in a vacuum furnace by first heating the raw article (to remove the rubber) at 550° C. for 4-5 hours, then heating at 1440-1450° C. for 8-10 hours, followed by cooling for 10-12 hours. The raw jewelry article is then obtained in step 118 for additional processing, as required.

FIGS. 2A-B depict manufacturing equipments connected with the steps shown in FIG. 1. Specifically, FIG. 2A shows a milling machine 202, sedimentation/separation equipment 204, drying equipment 206 and 212 and adding/sifting apparatus 208 and 210. FIG. 2B shows a molding unit 216, a vacuum furnace 218, a powder mixture 214 as well as raw jewelry articles 220. The density of the jewelry article formed is about 8.81 g/cm³ with an HRC hardness of about 74.0.

The manufacturing process described shows a 100 kg/day production capacity for powder mixture production. Also, the molding process has the capacity to handle 2500 pieces/mold in one day. Finally, the production of the raw jewelry article is about 5000 pcs/day.

Although the foregoing refers to particular preferred embodiments, it will be understood that the present invention is not so limited. It will occur to those of ordinary skill in the art that various modifications may be made to the disclosed embodiments and that such modifications are intended to be within the scope of the present invention. 

1. A method of forming a jewelry article comprising: providing a powder mixture comprising tungsten and one or more of: titanium carbide, chromium carbide, nickel, molybdenum, vanadium carbide and iron; placing the powder mixture in a mold; and applying sufficient pressure and temperature to the powder mixture to form a solid jewelry article.
 2. The method of claim 1, wherein powder composition comprises less than 50% tungsten by weight.
 3. The method of claim 1, wherein the powder composition comprises about 21-22% titanium carbide by weight.
 4. The method of claim 1, wherein the powder mixture comprises about 19-21% chromium carbide by weight.
 5. The method of claim 1, wherein the powder mixture comprises about 22-23% nickel by weight.
 6. The method of claim 1 wherein the powder mixture comprises about 7-8% molybdenum and vanadium carbide combined, by weight.
 7. The method of claim 1, wherein the powder mixture comprises about 2-3% iron by weight.
 8. The method of claim 1, wherein the mold comprises a cavity having an annular configuration.
 9. The method of claim 1, further comprising the step of adding a rubber material to the powder mixture before placing said mixture in the mold.
 10. The method of claim 9, wherein the rubber material comprises SBS.
 11. The method of claim 10, further comprising sifting the powder mixture before adding the rubber material.
 12. A jewelry article formed according to any one of claims 1 to
 11. 13. A jewelry ring formed according to the method of claim
 8. 14. A jewelry article comprising about 20-50% by weight tungsten and balance titanium carbide, chromium carbide, nickel, molybdenum, vanadium carbide and iron.
 15. The jewelry article of claim 14, wherein said article comprises about 21-22% titanium carbide by weight.
 16. The jewelry article of claim 14, wherein said article comprises about 19-21% chromium carbide by weight.
 17. The jewelry article of claim 14, wherein said article comprises about 22-23% nickel by weight.
 18. The jewelry article of claim 14, wherein said article comprises 7-8% molybdenum by weight.
 19. The jewelry article of claim 14, wherein said article comprises 2-3% iron by weight.
 20. The jewelry article of claim 14, wherein said article has a density of about 8-9 g/cm³. 